Section 05 - Tripping & Backreaming Practices

1/68© K&M Technology Group - 2008

This is the most important subject of this school– The practices used by most groups are completely inappropriate– The serious problems experienced are self-inflicted, and

unnecessary

This section will cover:What is required for safe tripping

PracticesBHA requirements

BackreamingIs it good or bad ?Why do you see what you do ?How to do it safely (and when to do it)

Tripping & Backreaming Practices


Tripping & Backreaming Practices• Back-reaming or pumping out should be avoided

whenever possible in high-angle wells– The ability to trip out without pumping or backreaming is a

critical objective– Choosing any practice or equipment that forces you to

backream to trip out makes a mockery of risk-management• Because back-reaming and/or pumping out are the single-most

dangerous operation in any ER well– Maximum risk of stuck pipe, and of destabilizing the wellbore– It is also time consuming, and destructive on BHA equipment

– Engineers :• It’s not just a matter of circulating more … it’s a design issue too


Classic train-wreck story

• K&M see / review a lot of high-angle train wrecks– Most have almost identical chain-of-events– 2 common themes :

• Those that had bad hole cleaning while drilling (but they thought it was good). These also tend to have poor tripping practices.

– More common with motor BHAs– Note – Can have good hole cleaning with motors !!

• Those that had good hole cleaning while drilling, but still have poor tripping practices.

– This has become the most common of the two, ever since RSS became popular

– Does the following sound familiar ?


Say operator is drilling high or medium angle hole

1. No problems drilling to TD• Good hole cleaning while drilling, and no cavings reported

• How do they know it was good hole cleaning ?

• No tight hole at connections

• Good cuttings flow


2. At TD, hole is cleaned up• Multiple bottoms up circulated at TD

• Shakers clean up quite soon … team thinks hole must be clean

• In reality, hole cleaning system has shut down when low-RPM used for clean-up cycle

3. Trip commences• Soon pulls tight.

• Attempt to back-ream thru tight spot

• Hole packs off (initiating circulation or soon after)

• 1st cavings reported at this point


4. Back-reaming continues …• Packing off all the way to the shoe

• Relatively little cuttings while back-reaming, until ≈ 30o, then shakers blind with lot’s of cuttings… and cavings.

• Packs off also inside casing

5. Trip Back In

• For some reason, the trip back-in is whistle-clean…despite the nightmarish trip out…



What we will cover in this section:• Part 1 – What is happening downhole• Part 2 – How to enable tripping on elevators• Part 3 – Tripping procedures• Part 4 – Backreaming procedures



• Part 1 – What is happening downhole– How does the cuttings bed & BHA interact when tripping ?

• Trouble-free tripping, vs tight hole• Normal tripping vs. Back-reaming vs. Pumping Out

– Separating myth from reality– Why do we see what we see ?


What happens downhole when POOH ?

Most people visualize that tripping looks something like this …

And that “tight hole” looks like this …

If this is correct, then normal reactions are valid• Drop down a few feet, and commence back-reaming thru obstruction


What really happens downhole when POOH ?

What happens downhole when tripping in a deviated well ?– Firstly, assume that the hole is NOT 100% clean

– Even with a thorough clean-up– Even with Rotary Steering Tools !

– The BHA does NOT pull cuttings up the hole– Cuttings flow around the BHA, until they become too compressed– BHA design is critical to “flow around” ability– Has significant implications for how to manage tight hole


What happens downhole when POOH ?

• When pulling out, the BHA pulls up through the dirt …• For a trouble-free trip, the dirt must flow around the BHA as the

BHA moves through the bed

Video Clip


What really happens downhole when POOH ?

The dirt must be able to flow through the bit & BHA• Just like mud, we have a serious problem when the dirt can’t get past the BHA• Consider ketchup / sauce poured through a kitchen funnel


When driller sees tight hole …what is happening downhole ?

Video Clip

If this component blocks the flow of dirt, then tight hole looks like this …

But if this component blocks the flow of dirt, then tight hole looks like this …


What is tight hole ?Note that this volume of dirt is small …

• Only requires kilograms (not tons) to be stuck)

Unfortunately, this is the most common situation• Because of typical bit & BHA designs

•If you pull too far, you can’t go back down

•Turning pumps on is worst-possible response to tight hole


Backreaming PracticesWhat is backreaming?

Standard trip – no rotation or circulation, harmless cuttings bed by-passed

Backreaming – rotate and circulate while POOH, cuttings bed fully removed from the bottom of the hole. Cuttings drop out to form a dune above the BHA

Video Clip


Backreaming Practices


Backreaming PracticesPumping Out is Even Worse!

Pumping Out – dirt still piles up behind the BHA due to high velocity around the bit, stabilizers, and drill collars, but the conveyor belt is off!

Video Clip


Backreaming Basics

• What are the downsides/risks associated with Backreaming?– Stuck pipe– BHA equipment failures due to vibration– Key seating– Lost returns (if packoffs exceed fracture gradient)– Self-inflicted wellbore stability problems


Backreaming Basics

• Backreaming itself doesn’t damage the wellbore…– Rather, it is the Hydraulic Hammer effect that causes all the

problems…– Sudden large ECD pressure shock below pack-off

• Same principle will destroy pipelines, power stations, etc ...Why expect it to be less severe in a wellbore?

• These are often too large for PWD to measure


Hydraulic Hammer

• What PWD sees when hydraulic hammer occurs …• Pressure spikes are often “off the scale”• Remember, when you see a pack-off at surface, you only see

what’s left are dampening thru the bit, BHA & drillstring

3 pp

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Normal drilling ECD … How bad was this ECD spike ?


Backreaming Basics

• Interpretation of “wellbore stability” problems changes entirely if the wellbore has been “Hammered”– Often, the presence of cavings after packoffs is perceived as

the very cause of the packoffs• K&M contend that it is more likely the packoff created the cavings

due to the hammer effect• Evidence of this is “wellbore stability” problems often go away when

tripping practices are modified (due to avoidance of packoffs)



• Part 2 – How to enable tripping on elevatorsMany operators say “don’t back-ream unless you have to …”But experienced ER people “know” that no-matter what the

procedures say, that’s the only way they can get out of the hole

The ability to trip regularly on elevators is possible – But simply circulating more isn’t the answer


How clean must the hole be for tripping ?− It depends on the bit & BHA ...

• Junk slot area affects how thick a safe cuttings bed can be.


BHA components are critical to ability to trip


BHA components are critical to ability to trip

• Unless the BHA components are addressed as a high priority ….– Conventional tripping may be impossible despite best practices– It only takes one component to make a BHA un-trippable

• No matter how much circulation is done

– This makes a mockery of every risk management precaution we make, if this isn’t addressed as the highest priority

THIS IS THE SINGLE BIGGEST THING YOU CAN DO TO REDUCE (OR INCREASE) RISK IN YOUR PROJECT


BHA design for tripping

What needs to be done to bit & BHA ?– Junk-slot-area & junk-slot-tortuosity are key BHA

design priorities• Remove sleeve stabilizers on big-OD collars

– 6¾” tools for 8½” hole, 5” tools for 6 ½” hole– Especially on RSS, motors and MWD-LWD tools– Shoot for a minimum of 30% open area

• Or downsize to smaller collars– Eg. 6 ¼” tools instead of 6 ¾” for 8 ½” hole (or drill 8 ¾”)

• Replace sleeve stabilizers with integral blade stabilizers


Sleeve vs. Integral Blade

How a Sleeve Stabilizer sees the hole

How an Integral Blade Stabilizersees the hole


Component Trip-ability Example

Consider this New Zealand ER Well…• 9 1/2” tangent to ±6100m (20,000’) MD• Excellent HC parameters

o 700 gpm / 150 rpm o 3xBU cleanup cycles, shakers clean after 2xBU

• Previous wells have never had problems trippingo Identical fluids, practices, drillpipe, BHA…


Bit #15 Blade, 14.5in2

Bit #38 Blade, 20.9in2

Bit #29 Blade12.5 in2

…However, the bits have changes “a bit”…


Trip #1 (5 Blade, 14.5in2 JSA)No problems, very similar to behavior on first well (similar bit)Minor 20-30k “peak” over pull in places (fairly slick on average)Average FF = 0.16 – 0.18

Trip #2 (9 Blade, 12.5in2 JSA)Long and troublesome trip with several intermediate circulation points required due to 50-60 k overpull in several locationsAverage FF = 0.19-0.20

Trip #3 (8 Blade, 20.9in2 JSA)Very smooth trip with the fewest number of tight spots of all the trips out. “Peak” overpull of <15k.Average FF = 0.16-0.18


Bit Design for Tripping

– Straighten up highly tortuous components• Eg. Tight-spiral long-gage bits


Prioritize Bit Junkslot Area– Steel body bits have much larger JSA than Matrix– Better impact resistance with Steel too

12 ¼”, 6-Blade Steel Body Bit54.3 in2 JSA (46%)

12 ¼”, 6-Blade Matrix Body Bit39.2 in2 JSA (33%)

Bit Design for Tripping


BHA Design for Tripping– A very effective option to enable normal tripping with

“tight” components is to enlarge the hole • Using Ream-While-Drilling (RWD) under-reamers• Very popular in the North Sea


Under-Reamer Considerations

How the BHA sees a “Dirty”under-reamed hole….

How Casing sees a “Dirty”under-reamed hole…

• K&M recommend this as a short-term “band-aid”, until the root cause is fixed, due to side effects of using RWD

– The danger of this technique is the “false sense of security”gained from a trouble-free trip out prior to running casing…

Video Clip


Hole Cleanup Practices

The hole must be cleaned up prior to tripping

• To be successful, the following is necessary :– Conveyor belt must be turned on (> 120 rpm)– Sufficient circulation is required

• Multiple BU required at > 120 rpm• Looking for at least 2 waves

• Remember saltation flow side-effects


Cleaning up for a trip

• The Conveyor belt requires > 120 rpm • Common directional-drilling practice ….

•RPM is often slowed whenever off-bottom (see next slide)•Hence, hole cleaning system is shut-down, convincing the team that the hole is clean

• Cuttings don’t know if the bit is on or off bottom !!• Conveyor belt must be on when bit is off-bottom too.

This is one of the most common mistakes … and one of the most illogical ones too !!


RPM vs Time log - Clean up on 18 July

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RPM rpm

RPM drops from 138rpm to 80+ rpm.Cleanup is therefore largely non-existant, and tripping starts in dirty hole

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Time-log showing RPM at end of drilling, and then during clean-up cycle

• Drilling RPM = 138, clean-up RPM only 80 – 90

• Shakers cleaned up soon ... hole was interpreted as clean

• This was their expected result since they were using a rotary-steerable !

• Or did the hole cleaning system just shut down ?

End Drilling / Start Clean-up



How much clean-up is necessary ?Cleaning up takes time

– Bottoms up is irrelevant for high angle wells• Expect 2 – 4+ x BU for cleanup time

– This is very sensitive to angle above 70o (see next page)– Patience is critical

• AND only “conveyor belt ON” time counts– Circulation time at < 120 rpm is irrelevant and wasteful


Effective Circulation Volume vs. Angle20,000' (6000m) tangent length, shallow KOP

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This gives some feel for how much circulation is necessary for different angles

• Note – only convey or belt circulation counts !

This is a minimum volume requirement … the “talking” at the shakers takes priority in

decision-making.

Notice how “gut feel” and “experience betray you, once angle gets > 70o



– You are looking for at least 2 waves of cuttings• Saltation flow side effect• If you’ve been drilling start-stop style, then expect more waves


A 2nd wave of cuttings flow is very common, if circulation continues (with the conveyor belt on)

• Similar to gravel packing, in reverse

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Normal circulation

At > 80o, 2nd wave is often after 3rd bottoms up

Times bottoms up

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• It’s easy to get suckered-in to stop clean-up when 1st wave finishes at ≈ 1 x BU

• Shakers will reduce to a background level (fines will never clean up)

• If there are still cuttings still on the shakers, the hole is NOT yet clean …

– Pay now, or pay later (with interest) !



Cleaning-up for a trip– This process does leave cuttings in the hole– The hole doesn’t have to be completely clean. – The goal is to have trouble free trips.


Tripping practices

When hole has cleaned up …– Trip out on elevators

(i.e. no pumping or backreaming)

– Back-reaming is only to be used as a last-resort option (more later)


• Part 3 – Tripping Out Procedures– Following the road-map

• How to identify “abnormal” from “normal”• How to identify “a ledge” from “cuttings”

– How to respond to tight hole• Do’s & Don’ts

– Pipe Stretch discussion


Tripping Out Procedure

1. Pull out of hole without rotation or circulation• Trip speed is important … controls speed of dirt flow

through the stabilizers & bit• Tighter BHAs require slower speeds

2. Monitor P/U weight while tripping out of hole• Compare real-time to theoretical drag trends (“roadmaps”)• Must have a road-map to know what “normal” is

(see following plots)


Using Road-Maps

1. If you are to make wise decisions about when “something is abnormal”, you need to know what normal looks like …

Experienced hands assume that they know this… “I don’t need a computer to tell me when I’ve got tight hole”

2. People also assume that they are looking for a sudden change

Both of these are vertical hole logic, and are perhaps the most common reason wells get into trouble while tripping

• If we had a genuinely clean hole, and “ledges” were the problem, then this logic is OK

• But remember we are looking for dirt build-up between stabilizers, which happens gradually

Video Clip


15k Here is a trip out, plotted against depth• Is this OK ?

But this is about to get stuck …• Can’t you see the train-wreck coming at you ?

This is the next stand pulled ?• What is the over-pull ?

• Looks like 15 k ?

In reality, hole is “talking” to you for +/- 10 stands•And overpull is 45k -lbs

45k

Classic indication of cuttings building up is diverging PU loads• Between “normal” and actual loads

• Usually over 4 – 5 stands


Tripping Out Procedure … continued

• If tight hole is encountered – Either via roadmap or not …

• For tight spot or increasing drag, always assume the problem is cuttings– Run in the hole 2 to 5 stands to get BHA away from tight

spot• If obstruction is dirt, you must un-pack the BHA before doing

anything else– If it took > 5 stands to pack the BHA, it will probably take that many

to un-pack it !!– Remember that cuttings can move down hole with BHA (in

avalanche regime <65°±)!



Tight Spot Procedure (…continued)

• Circulate & rotate at > 120 rpm for 30 minutes– Goal is to verify cuttings dune, so as not to waste time if otherwise– Conveyor belt must be on, if cuttings are to be moved

• POH carefully without rotation or circulation watching for the tight spot to recur

– If the tight spot has moved up hole, then obstruction was cuttings– Continue cleaning the hole up, per standard clean-up procedures



Tight Spot Procedure …continued

• If the tight spot has NOT moved up hole, then genuine tight hole is likely (key seat, ledge, swelling formation, etc.)– Circulating or backreaming may be used with caution – Must avoid pack-off while circulating or backreaming out of the hole

• Risk of stuck pipe• Pressure damage to wellbore below pack-off• Don’t want to lose returns

– Hole cleaning get’s really messy if we can’t circulate !


Pipe Stretch Implications- Vertical: Pick-up weight = Rotating wt = Slack-off wt- High angle: Weights are very different ….so what ?

Consider what’s actually happening downhole when the weight indicator changes when you kick the rotary on …- BHA immediately sucks up the hole, with missing force load

- typical stretch is 1’ per 1000’ MD (ie, 12’ at 12000’ MD)- If you rotate with any tension remaining …

- I think I’m stuck, will just make sure about that before I call somebody !


Pipe Stretch ImplicationsThe same thing happens while tripping in …

- How many times have you tried to roll off a “ledge” while tripping in?- What happens to the bit when rotation is imitated with the string in

compression?- The bit leaps forward, uncontrollably- This is a really good way to destroy a drillstring (if buckling is

present)!- Can also cause lost-returns due to surge effect


• Part 4 – Back-reaming Out Procedures– When is back-reaming OK ?– How to back-ream safely

• Do’s & Don’ts


Backreaming Basics

• Sometimes backreaming is necessary …– Tight hole on trips

–after verifying that the obstruction is NOT cuttings– Swabbing (can’t trip conventionally)– When removal of ALL cuttings is necessary

• To clean up hole for extreme casing runs in ER wells • Typical “trigger” is if casing run is so challenging as to require

flotation

• For production liner cement jobs, or running screens


When back-reaming, have you ever noticed ?....• Once you start back-reaming in a directional well, you can’t stop …until you

get to +/- 30o

– Actually, normal tripping can be resumed, with changes to normal practices

• You don’t see cuttings while backreaming, until you get to about 30o

– Then you get lot’s of cuttings suddenly

• Back-reaming was easier on lower angle wells ….

• The faster you go, the more problems you have ….

• Have you ever noticed severe cavings after back-reaming, despite never seeing them before hand ?

Back-reaming Introduction


Is back-reaming OK ?

• Firstly, let’s define what back-reaming is …– Tripping, while rotating & pumping – A means of fighting tight hole

• Back-reaming is not …– Working the pipe up (with rotation) during normal connections– When racking back stands during the clean-up process.


• What is K&M’s opinion on back-reaming ?– Dangerous, with high risk of stuck pipe, packing off, and

inducing wellbore failure (more later)• Only operation that has higher risk is pumping out !

– Tough on MWD & BHAs (vibration), and causes casing wear– Can be done safely …

• But needs to be done slowly to be safe• Practices must vary according to angle• Back-reaming is not faster than cleaning up thoroughly before

tripping

Back-reaming (continued)


BEACH

You must be pumping-out / backreaming slower than the dune

… remember the dune moves much slower for higher angles

How fast is safe to back-ream?

This is a good application for the bladed DP• Placed in the HWDP to move the dune faster

(if conveyor belt is on)

Pack-offs occur when the BHA is pumping-out or backreaming faster than the dune is moving


Backreaming Procedure• Clean hole up first• Never commence back-reaming while in overpull or tight hole

- BHA is literally embedded in cuttings- Consider pipe stretch: what direction does the BHA move if pipe is in

tension and we start to rotate?- Always drop down away from the tight spot before beginning to backream- Applies also to tripping in

- …. actually, this may be worse, since cuttings must now clear the bit & BHA pinch-points


Backreaming Procedure• Think of backreaming as drilling backwards

• Be patient - Backreaming must be done slowly- 10 min/stand sounds slow, but is equivalent to ROP of 600 ft/hr- Acceptable speed is very sensitive to angle when above 70o

- Dune will move slowly, especially if using low RPM- Pack-off will occur if pickup speed is too fast

• Very few options if lose returns


Effective Circulation Volume vs. Angle20,000' (6000m) tangent length, shallow KOP

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Back-reaming “safe speed” is driven by same “saltation flow” mechanism that drives how much circulation is necessary to clean the hole for a trip

Safe speed slows significantly beyond 70o


Remember Saltation Flow, and it’s side effectsThis has important implications for a drilling operation …

Side effect of back-reaming in a wellbore that has been cleaned-up

But saltation flow requires that the hole must re-fill to full drilling height, before you see cuttings at surface …

Imagine we have cleaned the hole up, and commence back-reaming from here …

This sucker-punches drilling operations all the time …

• You have back-reamed for 12 hours at slow ROP, and haven’t seen any dirt …•How do you interpret this … the hole must be clean

•So back-reaming get’s faster … and then the hole packs off


Backreaming Procedure

• Torque is primary tool to monitor pulling speed • If rig systems allow, consider pumping at drilling flowrate &

rotate at 120+ rpm (for larger hole sizes)- This will help disperse cuttings dune above BHA- However, hard on top drive & may cause casing wear- Alternative is low RPM while up-reaming, then high RPM down-reaming,

before final pick up to rack stand (without rotation– repeat cycle if tight)



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Packoff Tendencies (ie, BHA is colliding with cutting dune)


• Always clean up hole immediately after finish of backreaming -- never just pull out of the hole– Applies for cased hole as well as open hole– This explains the industries “typical” experience that once backreaming

starts, it can’t be stopped (in reality, all we need to do in order to return to tripping on elevators is erode the due away from the top of the BHA)

• Take special care coming into a casing shoe– Large OD rathole/washout accumulates cuttings– Consider extra circulation with rotation before proceeding



Backreaming Considerations• Under-reamers add an additional level of complexity /

risk to backreaming– Most RWD devices cannot be locked closed, causing vibration and un-

controlled hole enlargement / undercutting while backreaming (since the pilot BHA is unstabilized)

– One Exception is Halliburton’s XRReamer (drop-ball locking action)

Smith:Rinoreamer

Halliburton:XRReamer

AnderGauge:Anderreamer

Video Clip


Underreamer Considerations• Backreamed 8 1/2”x9 7/8” with RWD in string• Memory resistivity shows rugous and washed out hole after backreaming• Multiple packoffs and subsequent instability ensued on trip in

Intended Gauge Hole Diameter


A Final Word On Backreaming• Backreaming at high angle in larger hole sizes should be

thought of as “drilling backwards”- The cuttings dune is forced up-hole by the flow restriction

around the BHA

• Backreaming at 1-2 minutes/stand may not be enough time for the dune to “get out of the way”

• The time for patience is when backreaming to run casing


So, let’s talk about how this impacts what “good oilfield practice” means for different wells:•Consider our response to a major equipment failure …

• Lose 1 of 2 pumps (24hr repair)…

• Swivel packing leak (1hr repair)…

• Top Drive pinion gear breaks (3 day repair)…

• Washout in the drillpipe• 1000’ (300m) from surface…

• 1000’ (300m) above the BHA…

What should we do on a vertical well ?

What about a high angle well ?

What about a Medium angle well ?

Documents

Section 05 - Tripping & Backreaming Practices